Visual Illusions: Their Causes, Characteristics and Applications

by Matthew Luckiesh

In 1922, Matthew Luckiesh wrote an optical illusions book titled - Visual Illusions: Their Causes, Characteristics and Applications. It was probably the first book to comprehensively cover the topic of Optical Illusions, or Visual Illusions, as they were called then.

A version of the famous
Endless Stairs Illusion

Years of research preceded the writing of this optical illusions book. During those years the world became engulfed in "The Great War." Mr. Luckiesh worked on ways to camouflage our ships and airplanes using visual illusions. He dedicates a chapter to that topic.

On this optical illusion web site, we present this book to you, chock full of optical illusion information. It will be of interest to both the person who is fascinated by optical illusions and asks, "How do optical illusions work?" and also to the person doing serious research on the science of optical illusions. Some editing of the book has been done.

To navigate through it, click on a chapter link below. Once you have entered the chapter, navigate through the book pages by clicking on the numbers at the top or bottom of the page. The previous page title and the next page title appear as links to the left and right of these numbers.

Only a part of what is perceived comes through the senses from the object. The remainder always comes from within. Artists, architects, stage artists, magicians and camoufleur either take advantage of optical illusions or try to avoid them. They are vastly entertaining, useful, deceiving or disastrous, depending upon the viewpoint.~

Included in the introduction is a history of optical illusions and an initial discussion on understanding optical illusions.

How the human eye works is described. An eye diagram with the structure and parts of the eye is included. The eye anatomy section is followed by a discussion of how the eye plays a part in optical illusions.

The sense of sight differs considerably from the other senses. What we see with our eyes inside our head is projected outward and we have little consciousness of anything occurring inside our eyes. This makes it extremely difficult to convince ourselves that it is essentially a subjective sensation.

This chapter discusses how optical illusions are related to binocular vision, perspective, distance and size perception, and depth and stereoscopic vision.

This chapter of Visual Illusions discusses visual perception and optical illusions. Many figures apparently change in appearance owing to fluctuations in attention and in associations. Our perception is strongly associated with our accustomed ways of seeing objects. When the object is suggested it grasps our mind completely in its stereotyped form, resulting in what we call an optical illusion. The psychology of optical illusions is also discusses. The psychological hypotheses introduce factors such as judgment, will, attention and imagination. The physiological hypotheses depend largely upon such factors as accommodation and eye-movement.

Angles play an important part, directly or indirectly, in the production of optical illusions. The overestimation or underestimation of angles can result in what is referred to as a geometrical optical illusion. Discussed in this chapter are the twisted chord optical illusion, the spiral optical illusion, the pinwheel optical illusion along with the Zollner illusion, Muller-Lyer Illusion and the Joseph Jastrow Illusion.

When any of the ordinary criteria of relief or of distance are apparently modified, optical illusions of depth and distance are possible. There are many illusions of this sort, such as the looming of objects in a fog; the apparent enlargement of the sun and moon near the horizon; the flattening of the "vault" of the sky; the intaglio seen as relief; the alteration of relief with lighting; and various changes in the landscape when regarded with the head inverted. Certain data pertaining to the objects viewed must be assumed, and if the assumptions are incorrect, illusions will result. An increase in the brightness of an object is accompanied by an apparent movement toward the observer, and conversely a decrease in brightness produces an apparent movement in the opposite direction. H. A. Carr's report on optical illusions of distance, motion and movement is discussed.

Many interesting and striking illusions owe their existence to contrasts in brightness. A dark line or spot will appear darker in general as the brightness of its environment is increased; or conversely, a white spot surrounded by a dark environment will appear brighter as the latter is darkened. In other words, black and white, when juxtaposed, mutually reinforce each other. The visual phenomenon of irradiation (the apparent enlargement of a bright object when viewed against a dark background) does not strictly belong to this group, but it is so closely related to it and so dependent upon brightness-contrast that it is included.

There are almost numberless phenomena involving color, many of which are optical illusions, or seemingly so. It will be obvious that many are errors of sense; some are errors of judgment; others are errors due to defects of the optical system of the eye; and many may be ascribed to certain characteristics of the visual process. Substantial glimpses of the more important phases of color as related to illusions are presented in this chapter.

The lighting of objects or of a scene can alone produce an optical illusion. In still more cases, it can be a contributing factor in an optical illusion. All the illusions of brightness-contrast may be produced by lighting. Surfaces and details may appear larger or smaller, harsh or almost obliterated, heavy or light. This chapter of Luckiesh's optical illusion book discussed several aspects of lighting in relation to optical illusions.

Optical illusions abound everywhere. There are a number of special interest which occur in nature. The apparent form of the sky has attracted the attention of many scientific investigators for centuries. There are many conflicting opinions as to the causes of this appearance of form, but there is general agreement that the sky appears usually as a flattened vault. The flattened vault appearance of the sky is thought by some to explain the apparent enlargement of the sun, moon, and constellations when viewed at the horizon. In discussing the great illusions of nature, it appears appropriate to introduce the mirage. A mirage is not due to an error of sense of judgment. The eye sees what is presented but the inversions and other peculiar effects are due to variations in the refractive index of the atmosphere.

In the arts, forms, lines, perspective, contrasts, color and brightness are so important that it is obvious optical illusions are also important. Sometimes they are problems which must be suppressed. In other cases they are boons to the artist if he or she is equal to the task of harnessing them. Often they appear unheralded and unexpected. All the means for success which the painter possesses are also available to the decorator. However, the decorator may also make use of some of the optical illusions of irradiation, line, form, etc. which the architect uses.

Many illusions are found in architecture. Many of these were recognized long before painting developed beyond its primitive stages. The classic Greek architecture displays a highly developed knowledge of many geometrical illusions and the architects of those far-off centuries carefully worked out details for counteracting them. Drawings reveal many optical illusions to the architect, but many are not predicted by them. The ever-changing relations of lines and forms in architecture as we vary our viewpoint introduce many optical illusions which may appear and disappear. Any view of a group of buildings or of the components of a single building will exhibit some optical illusions. In reality we never see the same relations of lines, forms, colors, and brightnesses as indicated by the drawings or blue-prints. Perhaps this is one of the best justifications for the construction of expensive models of our more pretentious structures.

Many of the more notable magic optical optical illusion tricks were those involving the use of mirrors and the control of light. The mirror magic optical optical illusion has perhaps astounded audiences more than any other magic trick. In this magic optical illusion, a head, not attached to a body, seems to hover in a room. In this chapter you will find the famous magic optical illusion secret revealed.

In this optical illusion book, Matthew Luckiesh discusses camouflage as it occurs in nature and as it was used by the military during World War I. The name was coined by the French to apply to a definite art which developed during the "Great War" to a high state. It was during WWI that camouflage developed as a science. During World War II camouflage was developed to an even greater extent. It covers a vast field of activity in scientifically concealing and deceiving.